Molecular dynamics simulation studies of the ε-CL-20/HMX co-crystal-based PBXs with HTPB

Insight into Formation, Synchronized Release and Stability of Co-Amorphous Curcumin-Piperine by Integrating Experimental-Modeling Techniques

Intermolecular interactions between drug and co-former are crucial in the formation, release and physical stability of co-amorphous system. However, the interactions remain difficult to investigate with only experimental tools. In this study, intermolecular interactions of co-amorphous curcumin-piperine (i.e., CUR-PIP CM) during formation, dissolution and storage were explored by integrating experimental and modeling techniques. The formed CUR-PIP CM exhibited the strong hydrogen bond interaction between the phenolic OH group of CUR and the CO group of PIP as confirmed by FTIR, ss 13C NMR and molecular dynamics (MD) simulation. In comparison to crystalline CUR, crystalline PIP and their physical mixture, CUR-PIP CM performed significantly increased dissolution accompanied by the synchronized release of CUR and PIP, which arose from the greater interaction energy of H2O-CUR molecules and H2O-PIP molecules than CUR-PIP molecules, breaking the hydrogen bond between CUR and PIP molecules, and then causing a pair-wise solvation of CUR-PIP CM at the molecular level. Furthermore, the stronger intermolecular interaction between CUR and PIP was revealed by higher binding energy of CUR-PIP molecules, which contributed to the excellent physical stability of CUR-PIP CM over amorphous CUR or PIP. The study provides a unique insight into the formation, release and stability of co-amorphous system from MD perspective. Meanwhile, this integrated technique can be used as a practical methodology for the future design of co-amorphous formulations.

Molecular dynamics simulation of CL20/DNDAP cocrystal-based PBXs

CONTEXT

CL-20/DNDAP cocrystal is a promising new type of explosive with exceptional energy density and detonation parameters. However, compared to TATB, FOX-7 and other insensitive explosives, it still has higher sensitivity. In order to decrease the sensitivity of CL20/DNDAP cocrystal explosive, in this article, a CL20/DNDAP cocrystal model was established, and six different types of polymers, including butadiene rubber (BR), ethylene-vinyl acetate copolymer (EVA), polyethylene glycol (PEG), hydroxyl-terminated polybutadiene (HTPB), fluoropolymer (F₂₆₀₃), and polyvinylidene difluoride (PVDF), were added to the three cleaved surfaces of (1 0 0), (0 1 0) and (0 0 1) to obtain polymer-bonded explosives (PBXs). Predict the effects of different polymers on the stability, trigger bond length, mechanical properties, and detonation performance of PBXs. Among the six PBX models, CL-20/DNDAP/PEG model exhibited the highest binding energy and the lowest trigger bond length, indicating that CL-20/DNDAP/PEG model had the best stability, compatibility, and the least sensitivity. Furthermore, although the CL-20/DNDAP/F₂₆₀₃ model demonstrated superior detonation capabilities, it should be noted that this model displayed low levels of compatibility. Overall, CL-20/DNDAP/PEG model exhibited the superior comprehensive properties, thereby demonstrating that PEG is a more suitable binder option for PBXs based on the CL20/DNDAP cocrystal.

METHODS

The properties of CL-20/DNDAP cocrystal-based PBXs were predicted by molecular dynamics (MD) method under Materials Studio software. The MD simulation time step was set at 1fs and the total MD simulation time was 2ns. The Isothermal-isobaric (NPT) ensemble was used for the 2ns of MD simulation. The COMPASS force field was used, and the temperature was set at 295K.

The influence of temperature and component proportion on stability, sensitivity, and mechanical properties of LLM-105/HMX co-crystals via molecular dynamics simulation

Based on molecular dynamics (MD) simulation, the binding energy, cohesive energy density (CED), bond length, and mechanical parameters were calculated for 2,6-diamino-3,5-dinitropyrazine-l-oxide (LLM-105) crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal, and their co-crystals under different temperatures. Three LLM-105/HMX patterns were constructed to investigate the influence of component proportion on structures and properties of co-crystals, in which the mole ratios of LLM-105 and HMX are 1:1, 1:2, and 2:1. The effect of temperature and components on the stability and sensitivity were investigated as well. The results show that the binding energies, CED and mechanical parameters of all the co-crystals, decrease when the temperature increases from 248 to 398 K, while their maximum N-NO₂ bond length (L_max) increases with rising temperature, indicating that the sensitivities increase and stabilities decrease when temperature rises. At all temperatures, co-crystals exhibit larger CED and shorter bond length than that of single explosive, demonstrating that they are more stable and less sensitive than single crystal, where the stability of co-crystals was ordered as 2:1>1:1>1:2. Moreover, the bulk modulus (K) and shear modulus (G) of co-crystals are lower than that of HMX, conversely, the Cauchy pressure and K/G are higher than that of HMX, implying co-crystals have better ductility. Finally, the 2:1 ratio of LLM-105/HMX co-crystal was identified as the excellent one, owning to the highest binding energy, highest CED, shortest L_max, and greatest ductility. Graphical Abstract Models of LLM-105/HMX and one of the properties.

Theoretical investigation into the influence of molar ratio on mixture system: α, γ, δ-HMX molecules coexisting with β-HMX crystal

Molecular dynamics (MD) simulation was conducted to research the effect of molar ratios for α/β-HMX, γ/β-HMX, and δ/β-HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) mixture systems on thermal stability, sensitivity, and mechanical properties of explosives, and the computing models were established by Materials Studio (MS). The binding energies, the maximum trigger bond length (L_N-NO2), cohesive energy density as well as mechanical properties of the mixture systems and the pure β-HMX crystal were obtained and contrasted. The results demonstrate that the molar ratios have great influence on the binding capacity of molecules between α, γ, δ-HMX, and β-HMX in the mixture systems. The binding energies decrease with the increase of molecular molar ratio and have the maximum values at the 1:1 M ratio. The maximum trigger bond length does not change apparently after mixing, while the cohesive energy density (CED) increases as the molar ratio increases but are all smaller than the pure β-HMX crystal, demonstrating that the sensitivity of the mixture systems increases. The mechanical properties decrease after mixture, which illustrates that the mechanical properties of the pure crystal are superior to the mixture systems.

Molecular dynamics simulations for CL-20/TNT co-crystal based polymer-bonded explosives

Molecular dynamics (MD) simulations were carried out to study the polymer-bonded explosives (PBXs) where the explosive base was the well-known high energy co-crystal compound, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT), and the polymer binders were fluorine rubber (F[Formula: see text], fluorine resin (F[Formula: see text], polyvinyl acetate (PVAc) and polystyrene (PS), respectively. The binding energies, pair correlation functions (PCFs) and mechanical properties of the PBXs were reported. According to our theoretical results of binding energies, the compatibility of the PBXs is predicted to be in the following order: CL-20/TNT/PVAc[Formula: see text] CL-20/TNT/F[Formula: see text] [Formula: see text] CL-20/TNT/PS [Formula: see text] CL-20/TNT/F[Formula: see text]. The binding energies of the PBXs on three crystalline surfaces, (100), (001), (010), of the CL-20/TNT co-crystal were also compared: CL-20/TNT(100)[Formula: see text]CL-20/TNT(001)[Formula: see text]CL-20/TNT(010) for F[Formula: see text], F[Formula: see text], and PS; CL-20/TNT(001)[Formula: see text]CL-20/TNT(100)[Formula: see text]CL-20/TNT(010) for PVAc. The PCF analysis reveals that there exist H-bonds between H and O, F, and N atoms on all three interfaces and among all H-bonds, N H-bond has the fewest number. For the CL-20/TNT co-crystal, the moduli can be reduced by adding a small amount of the polymer binders but the ductility can be prolonged only by F[Formula: see text] and F[Formula: see text].

Crystal transition behaviors of CL-20 in polyether solid propellants plasticized by nitrate esters containing both HMX and CL-20

Co-crystal of CL-20/HMX was formed in NEPE propellants with the co-existence of CL-20 and HMX after curing for two weeks.